I was having a problem where my Samsung Android S6 was unable to connect to the T1d controller from within the Tello app. I have now fixed this and the T1d is now working as intended.

Here is the fix for anyone having a similar problem.

Symptom:

Inside the Tello app, you can see nothing in the Bluetooth settings tab, i.e. no devices to select to connect to, only the picture of the controller and the how to connect steps.

Steps:

1) Double check that Bluetooth is active on the phone (i.e. you can see the controller from within your phone's own bluetooth connections outside the Tello app).

2) In the Tello app, go back to the main page, and in the top centre there are some icons for wifi (drone connection), Bluetooth etc

3) If the Bluetooth icon here is grey, then Bluetooth isn’t being passed to the app correctly, even though you have made sure it is turned on in step 1.

4) When you first installed the app, it asked you to give access to a variety of phone functions. Sometimes this doesn’t work properly because the app boots up before finishing asking or your phone has more restrictions outside the app.

5) To check or fix this, go into you phones settings, and look for the application settings, and find the Tello app. There should be a permissions setting under this. Check that it has access to everything, and especially make sure it has Bluetooth requested (I had to grant additional access here, even after accepting all 4 requests from within the Tello app).

6) Restart the Tello app. You should now be able to see your T1d in the Bluetooth settings tab of the Tello app.

7) Another option to try is uninstalling and reinstalling the app which can trigger not only the latest app and clean permissions, but any necessary firmware updates.

I also experienced these kinds of issues trying to connect the GameSir T1 controller and what temporarily appears to have resolved the issue is I connect the Remote Controller by Bluetooth immediately before launching the Tello Application. I never see on my phone screen that the RC is actually connected, even after I first paired the device the status displayed simply just shows connecting in process. I then power on the Tello and connect before I open the Tello App. Once in the App and connected I go to Bluetooth Controller and finally it shows up. The trick here is to tap on the right side area where it says disconnected. There's a brief pause followed by icon displaying now connected. Doing the steps that way I've seen the RC connect easier and quicker than following the instructions provided through the Application.

I have the same problem, with an Xperia XZ, android 8.0. The bluetooth icon stays grayed out in Tello app. Permissions are fine, bluetooth is turned on on the phone, Tello is connected via wifi, controller turned on, nothing happen

Yup - same problem. I cannot pair the controller with my Samsung S9+ or two other models of Android phones and the Bluetooth stays greyed out in Tello and the controller does not show up in the Bluetooth list in Trello. Very frustrating.

Finally solved it with help from https://www.youtube.com/watch?v=RltYL1og38U

Process:
1. Ensure Location is turned on in the Tello app (but location services don't seem to need to be turned on on your phone). Without Location being turned on the controller will not connect.
2. Turn on Blue tooth on your phone (if not already on)
3. DO NOT attempt to pair the controller with Bluetooth
4. Turn on your Tello
5. Connect to the Tello drone through Wireless
6. Launch the Tello app and go to -> Settings -> Bluetooth Controller Settings
7. The Gamesir will be listed and showing Disconnected
8. Tap the controller name and it will connect to the controller
9. Exit from Settings and you should be good to go